1. Field of the Invention
The present invention relates to the field of semiconductor manufacturing techniques and, more particularly, to a technique for dispensing slurry for polishing wafers.
2. Prior Art
The art abounds with references pertaining to techniques for polishing a surface. Various semiconductor polishing techniques today can be traced back to the polishing methods employed to polish optical lenses. Similar techniques have been utilized in the semiconductor field to polish wafers, which are used for manufacturing integrated circuit devices. Thus, a number of methods are known in the prior art for polishing wafers.
The manufacture of an integrated circuit device requires the formation of various layers (both conductive and non-conductive) above the base substrate to form the necessary components and interconnects. During the manufacturing process, removal of a certain layer or portions of a layer must be achieved in order to pattern and form various components and interconnects. Generally, this removal process is termed "etching."
One of the techniques available for removing material is the chemical-mechanical polishing (CMP) process in which a chemical slurry is used along with a polishing pad. The mechanical movement of the pad relative to the wafer provides the abrasive force for removing the exposed surface of the wafer. A variety of CMP tools are available to perform this type of polishing. Improvements are currently being sought in the areas of pad design, chemical compositions of the slurry and forces exerted on the wafer by the pad, all to obtain better control over existing CMP practices. However, one area lacking consideration is the area pertaining to the storage, mixing and transport of slurry to the pad for use on the tool.
The current practice entails premixing of a slurry in relatively large quantities (1 to 15 +gallons) prior to use. Generally, bulk slurry is taken from storage in large quantities and premixed to a desired concentration. The mixing will depend on the type of use for the slurry. For example, in performing CMP on oxides, generally, slurries are diluted to desired concentration, typically by the use of de-ionized water. In performing CMP on metals, oxidizers and/or etchants are generally used to control the chemical component of the polishing process. Dilution by the use of de-ionized water can also be practiced.
Furthermore, additives can be introduced as well, for both oxide and metal polishing, if required. These additives are utilized to enhance removal rate, uniformity, selectivity, etc. Then the slurry is heated, if necessary, and retained in a container for transport to the pad. This results in variable heat loss during distribution to systems located in different environments or at varying distances. The technology is further complicated by a potentially short lifetime of the slurry after addition of chemical oxidizer, etchant and/or additive. Additional risks are encountered if either the slurry or oxidizer/etchant/additive (or the combination of slurry and oxidizer/etchant/additive) experiences degradation at elevated temperatures or over prolonged period of time.
Also, to change concentration of the dilution or chemicals, usually the entire system must be purged and the mixture disposed of and remixed at the desired concentrations. In some instances, concentration levels will change due to evaporation of the diluting agent, such as water. This constant remixing of the chemicals can be a significant cost burden in manufacturing.
Therefore, it is appreciated that a novel technique for providing slurry distribution in order to reduce waste and improve control over the slurry is desirable. The present invention addresses these needs.